Gary Frazier and James Luscombe of Texas Instruments have developed one embodiment of a quantum effect switching device which utilizes a dumbbell-shaped column structure to create a three terminal switching device which uses quantum effects. This embodiment is described in Frazier and Luscombe's co-pending application, Serial No. 07/608,509, entitled "Quantum Effect Switching Device", filed concurrently herewith and assigned to the Assignee of the present application, the disclosure of which is hereby incorporated by reference into the present application.
The creation of column structures such as those described herein requires an etchant process which exhibits an extremely high level of anisotropy. There is a certain degree of tradeoff between selectivity and anisotropy in the selection of an etchant process to form these column structures. As such, an etchant process such as a boron trichloride reactive ion etch which exhibits an extremely high level of anisotropy exhibits a large component of ion impact etching during the etch operation. Because of this high component of ion impact etching, extremely robust mask materials such as metal have been used to create these column structures. The use of metal as an etch mask has been very successful in the creation of single column structures and has the added benefit of creating a contact point on the top of the column structure. However, when a dumbbell-shaped column structure is desired, the use of a metal mask creates a short across the two columns preventing separate electrical contact at each of the columns.
Accordingly, a need has arisen for a process which allows for the highly anisotropic formation of double column structures but which does not use mask materials which electrically short the entire outer surface of the column structure.